手写ArrayList集合

小咪咪 2022-03-20 15:46 275阅读 0赞

### 1.手写ArrayList集合需要实现的接口 ###

package com.weichai.arraylist;
    
    /**
         *   自定义手写ArrayList接口
     * @author linhaiy
     * @date 2019.02.12
     * @param <E>
     */
    public interface ExtList<E> {
    
    	public void add(E object);
    	
    	public void add(int index, E object);
    	
    	public Object remove(int index);
    	
    	public boolean remove(E object);
    	
    	public int getSize();
    	
    	public Object get(int index);
    }

### 2.手写ArrayList集合具体实现 ###

package com.weichai.arraylist;
    
    import java.util.Arrays;
    
    /**
        *    纯手写ArrayList
     * @author linhaiy
     * @date 2019.02.12
     * @param <E>
     */
    public class ExtArrayList<E> implements ExtList<E> {
    
    	private transient Object[] elementData;        // 保存ArrayList中数据的数组
    	private int size;                              // ArrayList实际数量
    	
    	public ExtArrayList() {
    		// TODO Auto-generated constructor stub
    		this(10);                                 // 默认初始容量为10
    	}
    
    	public ExtArrayList(int initialCapacity) {
    		// TODO Auto-generated constructor stub
    		if(initialCapacity < 0) {
    			throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
    		}
    		elementData = new Object[initialCapacity];      // 初始化数组容量
    	}
    
    	public void add(E object) {
    		// TODO Auto-generated method stub
    		ensureExplicitCapacity(size + 1);
            elementData[size++] = object;
    	}
    
    	public void ensureExplicitCapacity(int minCapacity) {
    		// TODO Auto-generated method stub
    		// 如果存入的数据,超出了默认数组初始容量 就开始实现扩容
    		if(elementData.length == size) {
    			// 获取原来数组的长度 2
    			int oldCapacity = elementData.length;      
    			// oldCapacity >> 1 理解成 oldCapacity/2 新数组的长度是原来长度1.5倍
    			int newCapacity = oldCapacity + (oldCapacity >> 1);   
    			if(newCapacity < minCapacity) {
    				// 最小容量比新容量要小的,则采用初始容量minCapacity
    				newCapacity = minCapacity;
    			}
    			elementData = Arrays.copyOf(elementData, newCapacity);
    		}
    	}
    
    	public void add(int index, E object) {
    		// TODO Auto-generated method stub
    		rangeCheck(index);
    		ensureExplicitCapacity(size + 1);
    		System.arraycopy(elementData, index, elementData, index + 1, size - index);
    		elementData[index] = object;
    		size ++;
    	}
    
    	public void rangeCheck(int index) {
    		// TODO Auto-generated method stub
    		if(index >= size) {
    			throw new IndexOutOfBoundsException("数组越界啦!");
    		}
    	}
    
    	public Object remove(int index) {
    		// TODO Auto-generated method stub
    		Object object = get(index);
    		int numMoved = elementData.length - index - 1;
    		if(numMoved > 0) {
    			System.arraycopy(elementData, index + 1, elementData, index, numMoved);
    		}
    		elementData[--size] = null;
    		return object;
    	}
    
    	public boolean remove(E object) {
    		// TODO Auto-generated method stub
    		for(int i = 0; i < elementData.length; i++) {
    			Object element = elementData[i];
    			if(element.equals(object)) {
    				remove(i);
    				return true;
    			}
    		}
    		return false;
    	}
    
    	public int getSize() {
    		// TODO Auto-generated method stub
    		return size;
    	}
    
    	public Object get(int index) {
    		// TODO Auto-generated method stub
    		rangeCheck(index);
    		return elementData[index];
    	}
    
    }

### 3.测试类 ###

package com.weichai.ArrayList_Write;
    
    import com.weichai.arraylist.ExtArrayList;
    import com.weichai.arraylist.ExtList;
    
    /**
        *    手写ArrayList测试
     * @author linhaiy
     * @date 2019.02.12
     */
    public class ArrayListTest {
    
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		ExtList<String> arrayList = new ExtArrayList<String>();
    		arrayList.add("张三");
    		arrayList.add("李四");
    		arrayList.add("王武");
    		arrayList.add(1, "海哥");
    		System.out.println("获取第一个元素值:" + arrayList.get(0));
    		System.out.println("获取第二个元素值:" + arrayList.get(1));
    		System.out.println("获取第三个元素值:" + arrayList.get(2));
    		System.out.println("获取第四个元素值:" + arrayList.get(3));
    		System.out.println("获取第五个元素值:" + arrayList.get(4));
    		
    	}
    
    }